A packaging machine of this kind is known, for example, from GB 1 373 203.
DE-A-195 16 871 likewise discloses a packaging machine for tubular bags, comprising a film feed device, a forming collar, a film transport device, a film joining device, a sensor device, a control device, and a tracking device. In this packaging machine the film transport device is disposed downstream of the forming collar, viewed in the material flow direction of the film web. The film web can be pulled over the forming collar by means of said film transport device. The film web can be shaped by means of the forming collar into a tube extending in the material flow direction. The film joining device is disposed downstream of the forming collar, viewed in the material flow direction of the film web. Opposite edge areas of the film web can be bonded together by means of said film joining device. Any misalignment of the film web perpendicular to the material flow direction of the film web can be detected by means of the sensor device and transmitted to the control device. The tracking device can be actuated by the control device in such a way as to counteract the misalignment of the film web perpendicular to the material flow direction.
JP-A-08 337 219 discloses an apparatus for manufacturing a cylindrical film. In this apparatus there is disposed downstream of a forming element, viewed in the material flow direction of the film material, a transport device which transports the film material. The film material can be shaped by means of the forming element into a cylindrical tube extending in the material flow direction and can be heat-sealed by means of a joining device disposed downstream of the forming element, viewed in the material flow direction. By means of a sensor device, any misalignment of the film material perpendicular to the material flow direction can be detected and communicated to a control device. The sensor device is disposed between the forming element and the joining device, viewed in the material flow direction. A tracking device can be actuated by the control device in such a way that the tracking device counteracts the misalignment of the film web perpendicular to the material flow direction. The tracking device is disposed between the forming element and the joining device, viewed in the material flow direction.
For forming a web-shaped packaging material into a tube, a film web is normally pulled over a forming collar. After the film web has been pulled over the forming collar, opposite edge areas of the film web are bonded together by means of a film joining device, thereby forming a tube. The tube is then sealed perpendicular to its longitudinal direction, filled from the top with an item to be packaged in the tubular bag and sealed again, this time above the now packaged item.
For various reasons it is possible that the film web, viewed perpendicular to the material flow direction of the film web, will become misaligned. If this is the case, the longitudinal seam of the tubular bag will not be properly produced, resulting in tubular bags that are untight or substandard because of the poor longitudinal seam. In the prior art a sensor device is therefore present by means of which the misalignment of the film web can be detected and a corresponding signal transmitted to a control device. The control device then actuates a tracking device such that it counteracts the misalignment of the film web perpendicular to the material flow direction.
Although the prior art packaging machine already works quite well, it does not yet operate completely satisfactorily. In particular, rejects or lower quality bags occasionally occur.